OK, I've been reading stickies and searching old threads for several days now. I have a pretty good grasp on how everything works, but I'm still confused about one thing. I know that the bin file is what is in the chip. So to start I need to download a bin, say ARAP (seems popular). I know that to read/edit the bin you need an editor with a definition file (ie. tuner pro w/ xdf). But I'm a little confused by all the talk of masks. My understanding is the mask is the program inside the bin that the ecm uses to interpret the bin data. Assuming that's true, does each bin have a particular mask? Can you change the mask in the bin? I know this is a real newb question, but several of the posts I've read seem to contradict each other when referring to the distinction between Bins, Masks, and Definition files.

Pick one that's as close to what YOUR combo is, not just because it's popular.

OK, The "mask" is a way of refering to the designator for which format, or layout, the code for that particular ECM is constructed. What appears at which address in the chip, which contains a binary representation of what the ECM is to do, and when to do it, with what.
Does the bin have a mask ? Well, yes, and no. The ECM will look for particular data at particular addresses in the bin, so the mask is a way of matching the bin layout to the ECM for which it was written. So, in a way, yes, and it must match the mask for the ECM.
Can you change it ? No. It's a layout of bits, not a thing that it read and acted on.

As to the contradictions, well.....
The definition files are written for particular data layouts in the bins, at particular addresses, so in a way the definition file must be written for a particular mask so that it looks in the bin at the right place for a thing.

Though not necessarily correct in every detail, I hopr that it's a little more "plain english" and does it help ?

Just a little confused why it's possible to use either $32B or $6E to the '165 ECM?

As above, the code layout is different, but not necessarily the hardware.

Think of it this way.
We have a "mask" W98 and we have a "mask" WinXP.
They both work on the same PC, but the code is completely different.
Then, we can have a "mask" MacOSX that runs on completely different hardware.
Does that help ?

That is a good way to explain it. You can run W98 on a computer that used W95. They can utilze the same hardware and produce the same outputs even though the actual software works differently. Same with the same "calbrations" (proper term) for $32, $32B and $6E.

But, Mac OS is designed for an entirely different computer (Macintosh). Think of this as SD with the 7730. Just like you cannot run Mac OS except a Mac, you cannot run $8D on a '165. There are other calibrations than the $8D such as $6D or $A1 that run on the 7730. Because they not used on TPI V8s (or even thirdgens) so you never see them discussed - but there are other calibrations that will also run on a 7730. Knowing this, lets you know the other cars (other than a late model 3rd Gen) where you can get a 7730 ECM from a wrecking yard should you ever need to replace it.

Lastly, some "calibrations" can work on different ECMs. The $8D can run on the '7730 (F-bodies) and '7727 (Vettes).

Clear as mud?